Multicasting is, in general, a term used to characterize communication between a single sending node and multiple receiving nodes on a network. Multicasting is used for a variety of purposes, such as updating mobile corporate employees from a home office, or publishing online newsletters. Typically, the receiving nodes are all members of a predefined multicast group.
Many multicasting techniques rely on the use of a multicast tree to disseminate a multicast message among the members of a group. A multicast tree is a communication topology in which the sender of the multicast message transmits the message to a subset of the nodes in the group. Each of the nodes that receives the message then forwards copies of the message to a second subset of nodes in the group. The second subset repeats this process, and so on, until the message reaches all of the members of the multicast group.
One of the challenges faced when multicasting a message via a multicast tree is how to recover from the failure of nodes in the tree. Because of the pyramidal structure of a multicast tree, the failure of even a single node to forward the multicast message can prevent many other nodes from receiving it.